This invention relates to electronic calculators, and more particularly to electronic display calculators of the nonprinting type.
Electronic display calculators, particularly those of the hand-held or pocket size, have achieved wide popularity in both business and nonbusiness applications particularly due to their low cost and convenient size. Such calculators are typically provided with a manually actuatable keyboard having a set of digit keys and functions keys, a visible multidigit display, typically comprising an LED display, a battery power source, and electronic circuitry usually embodied on a single integrated circuit chip for performing manually specified arithmetic and transfer functions on numeric data entered manually via the keyboard. Typically, the manually entered numeric data and the calculation results are displayed, while symbols representing the specified functions are not.
A serious disadvantage inherent in display calculators which is not shared by electronic printing calculators is the lack of capability for providing a quick check on the correctness of entry of the numeric data and also the correctness of entry of the specified functions. In an electronic printing calculator, for example, a printed tape is produced for all entries, which contains a permanent record of the entered data, the function specified by the operator and the calculation results. Thus, to check the correctness of a particular computation or series of computations, it is only necessary for the operator to view the printed tape. In a display calculator, on the other hand, no such permanent record is produced. Accordingly, the only way to check the correctness of a series of computations is to re-enter the numeric data and operate the function keys a second time in the proper sequence to check the result against the first computation. This is a time consuming process which effectively doubles the length of time required to perform a set of calculations and to verify the accuracy of the result. In addition, entry errors can be made by the operator when performing the second set of computations which then necessitates a third set of computations to arrive at a verified result.